Japan is the world's largest selenium producer. Japan exports 80% of its production of selenium. Selenium is mainly obtained as a by-product from copper electrolytic slime that is generated upon copper refining. Produced selenium is used in the fields of, for example, glasses, colors, and chemicals. It is said that eventually 6 t of selenium is discharged into water systems. Oxyanions, which are in the form of soluble selenate and selenite, have chronic/acute toxicity to organisms. Therefore, a strict uniform wastewater standard is set at 0.1 mg/L. At present, wastewater is cleaned by coagulation precipitation or chelate treatment; however, such treatment is problematic because of high cost. In these methods, resources are largely consumed and selenium cannot be recovered as a resource from chemical sludge or the like because of the low selenium content.
Non-Patent Literature 1 discloses reduction of selenate and selenite by means of Pseudomonas stutzeri. In addition, the present inventors isolated Pseudomonas stutzeri NT-I with an aim to develop a biological treatment method for a selenium compound (Patent Literature 1). Pseudomonas stutzeri NT-I is capable of efficiently reducing selenate into selenite and further reducing selenite into elemental selenium. Elemental selenium is water-insoluble and atoxic. Therefore, it would be possible to detoxify, for example, wastewater containing a selenium compound at relatively low cost and recover selenium from the detoxified product for recycling selenium with the use of Pseudomonas stutzeri NT-I. It is necessary to examine treatment conditions and develop facilities in order to carry out treatment of a selenium compound using a microorganism to efficiently recover selenium.